A bolt loosening test machine can be used to research looseness under the condition that a bolt bears the load, and the current bolt loading loosening test machines are classified into the following categories:
1. Junker Type Looseness Test Method
For example, GB/T 10431-2008. A Junker type looseness testing machine primarily applies an alternating transverse load to a fastener that applies a pretightening force to enable the fastener to move transversely. This transverse motion causes relative swing between a bolt and a nut, thereby resulting in greater micro slip of contact surface between threads and rapid looseness of the fastener. This allows the fastener to loosen faster than any previous test method.
2. Electro-Hydraulic Servo-Controlled Vibration Method
During test, a tested fastener is tightened on a clamping platform, and a specified pretightening force is produced. An alternating transverse displacement is produced between two clamped metal plates through a servo hydraulic cylinder, resulting in reduction or even loss of a clamping force. The instantaneous clamping forces are continuously recorded, and the anti-looseness properties of the fastener are judged by comparison.
3. NAS Vibration Test Method
A specimen is tightened into a test sleeve, and location marks are made on a part and the sleeve. Then, the sleeve is placed on a vibration testbed for moving back and forth. After starting, the sleeve impacts both ends of a guide back and forth in the guide, producing a large impact force and causing looseness of the specimen. During the test, the position change of the specimen is recorded with regular stop, and the anti-looseness properties of the specimen are judged accordingly.
All of the above test stations are intended for a single bolt loosening testbed, and bear single load. However, in the analysis of multi-bolt structures such as flanges, the load on the bolt cannot be simply and accurately equivalent to the single bolt due to the existence of the interaction between the bolts; and in the process of actual use of the bolts, in the case of a plurality of bolts, the load is generally complicated, and is not a single transverse load. Therefore, this testbed is designed to effectively simulate the actual load condition of the multi-bolt flange and to obtain the looseness of each bolt more appropriately when a plurality of bolts bear the load. At present, there is no relevant patent in the multi-bolt loosening test machine.